It has long been a goal of metallurgists to take low grade metals, such as low carbon steel, and turn them into high quality steels and more desirable products through inexpensive treatments, including annealing, quenching, and tempering to name a few. Previous attempts have met with limited success in that they did not always produce a desirable product.
It is a goal and an advantageous aspect of the present invention to provide an inexpensive, quick and easy way to produce a low carbon iron-based alloy containing bainite and/or martensite.
Processing of steel generally takes large pieces of equipment, expensive and dangerous heated fluids, such as quenching oils and quenching salts, and tempering processes which include the use of ovens and residual heat from pouring molten steel followed by quenching in order to raise the hardness of the steel to a desirable value. Bainite and martensite are very desirable materials, and they generally have Rockwell hardnesses of from about 40 and up.
Bainite is generally an acicular steel structured of a combination of ferrite and carbides that exhibits considerable toughness while combining high strength with high ductility. Usually formed by austempering, bainite is a very desirable product. The practical advantage of bainitic steels is that relatively high strength levels together with adequate ductility can be obtained without further heat treatment, after the bainite reaction has taken place. The steels are readily weldable, because bainite, rather than martensite, will form in the heat-affected zone adjacent to the weld metal, so the incidence of cracking will be reduced. Furthermore, the steels have a low carbon content, which improves the weldability and reduces stresses arising from transformation.
Martensite is another acicular steel made of a hard, supersaturated solid solution of carbon in a body-centered tetragonal lattice of iron. It is generally a metastable transitional structure formed during a phase transformation called a martensitic transformation or shear transformation in which austenized steel is quenched to a temperature just above the martensite range and held at that temperature to an equalized temperature throughout before cooling to room temperature. Since chemical processes accelerate at higher temperature, martensite is easily destroyed by the application of heat. In some alloys, this effect is reduced by adding elements such as tungsten that interfere with cementite nucleation, but, more often than not, the phenomenon is exploited instead. Since quenching can be difficult to control, most steels are quenched to produce an overabundance of martensite, and then tempered to gradually reduce its concentration until the right structure for the intended application is achieved. Too much martensite leaves steel brittle, too little leaves it soft.
Therefore, it is an aspect of the present invention to provide a method and apparatus for micro-treating low carbon iron-based alloys to contain a desirable quantity of bainite and/or martensite. The micro-treated low carbon iron-based alloy may have varying thicknesses for application and be readily weldable while having the high tensile strength, the ability to save material and to reduce weight.
It is a goal and an advantageous aspect of the present invention to provide an inexpensive, quick and easy way to produce a low carbon iron-based alloy containing bainite and/or martensite.